Filter cartridge incorporating a peripheral compatibility matrix

ABSTRACT

A filter assembly employs inward and outward radially displaced portions of a peripheral shoulder on the cartridge as components of a cartridge compatibility matrix. Alternative base assemblies include mounting structures complementary to the configuration of the peripheral shoulder to exclude incompatible cartridges. The peripheral shoulder is preferably a roll seam connecting first and second sections of the filter housing. The invention further contemplates a pattern of radial protrusions from a portion of the cartridge housing received in a base receptacle as part of a cartridge compatibility matrix. The base receptacle is configured to receive only those cartridges having a compatible pattern of radial protrusions. A cartridge compatibility matrix including both inward and outward deformations of a cartridge peripheral shoulder and radial protrusions of the received portion of the cartridge housing can ensure both cartridge compatibility and a particular mounted position of the cartridge relative to the base.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to fuel filters employed inconnection with internal combustion engines. More particularly, thepresent invention relates to replaceable fuel filter cartridges forremoving foreign particles and/or separating water from the fuel supplysystem of an internal combustion engine.

[0003] 2. Description of the Related Art

[0004] Fuel filter systems to which the invention relates commonlyemploy a disposable filter cartridge that is replaced at pre-establishedintervals of filter usage. The replaceable cartridge is conventionallysecured to a base that defines inlet and outlet connections between thecartridge and the fuel supply system. Numerous retention systems havebeen employed for securing the filter cartridge to the base and allowingremoval of the cartridge for replacement purposes.

[0005] In practice, filter cartridge requirements may vary dependingupon: the type and make of the internal combustion engine; the specificapplication for which the engine is employed; the climate in which theengine is operated; and/or regional characteristics as to the quality ofthe fuel supply. Filter cartridges suitable for replacement in aparticular filtration system, commonly vary as to capacity, fluidcompatibility and filter media qualities.

[0006] One of the recurring problems in assuring filtration systemperformance is encountered in connection with replacement of the filtercartridge. It is imperative that the replacement cartridge be compatiblewith the filtering requirements for the fuel system. It is common forfilter cartridges to have a generally similar exterior configurationregardless of performance. As a result, a replacement filter cartridgemay dimensionally conform to the base of a given fuel filter assembly,and not comply with the applicable specifications for the fuel systemand thereby jeopardize the integrity of the fuel filtering system.Replacement with an incompatible filter cartridge can have very seriousconsequences for the operation of the internal combustion engine and mayalso be unnecessarily more expensive than less costly cartridges whichare fully suitable. In practice, replacement cartridges may be sosimilar in overall configuration that the owner of the vehicle and/orthe maintenance technician servicing the internal combustion engine mayunknowingly jeopardize the integrity of the filtering system byreplacement with a wholly unsuitable cartridge even though theunsuitable cartridge at least cursorily appears to be suitable. Thereare also, of course, instances where inferior or improper replacementfilter cartridges are intentionally installed without the knowledge ofthe owner of the operator of the vehicle.

[0007] For many applications, it is also desirable that a cartridge bemounted to the base at a specific angular orientation so that warnings,directions and markings affixed to the cartridge may be properlypositioned to ensure visibility and maximize the chances of successfulinformation dissemination. For other applications, it is desirable thatthe cartridge be locked in position relative to the base such that thecartridge may not rotate with relation to the base.

[0008] U.S. Pat. No. 5,035,797, which is assigned to the assignee of thepresent invention, discloses a fuel filter assembly in which a basemounts to the vehicle and a disposable filter cartridge is suspendedfrom the base. The cartridge is retained to the base by a threadedcollar that engages against a protruding roll seam structure at theperiphery of the cartridge housing. The cartridge is replaced byloosening the threaded collar and dismounting the filter cartridge. Akey system is disclosed in which keys axially project from the basethrough corresponding slots in the end cap of the filter cartridgehousing. The dimensions and location of the axially projecting keysensure compatibility by interfering with mounting and sealing ofincompatible cartridges lacking the correct slot configuration. The keysinterlock with the slots to mount the cartridge at a fixed angularrelationship to the base.

[0009] U.S. Pat. No. 5,837,137, which is assigned to the assignee of thepresent invention, discloses a similarly configured fuel filtrationassembly (e.g., the cartridge is retained to the base by a threadedcollar) incorporating an alternative location and key system.Protrusions from a receiving surface of the base are received incorresponding dimples in the opposing end surface of the cartridge tolock the cartridge at a fixed angular position relative to the base. Theprotrusions interfere with the mounting and sealing of a non-compatiblecartridge having an incompatible pattern of dimples.

[0010] A further variation on ensuring compatibility in fuel filtrationassemblies similar to those described above is disclosed in U.S. Pat.No. 5,766,463, which is assigned to the assignee of the presentinvention. The disclosed fuel filter cartridge is formed from a pair ofshell sections joined along a roll seam to form the retaining shoulder.The generally cylindrical upper portion of the filter cartridge isreceived within the base. A plurality of arcuate protrusions radiallyproject from the cylindrical upper portion of the cartridge to bereceived in compatible tracks in the base. The protrusions are disclosedas part of a key code system including the key/slot system described inthe '797 patent. A keying system that relies on protrusions from thereceived portion of the cartridge housing may permit defeat of thekeying system by allowing a cartridge without the protrusions to bereceived in the keyed base without interference.

[0011] An alternative filter cartridge mounting system is disclosed inU.S. Pat. No. 6,187,188, also assigned to the assignee of the presentinvention. The roll seam at the junction of the cartridge housingsections is radially outwardly displaced to form a plurality ofretention tabs. The base includes a fixed retaining structure comprisinga retaining lip defining a plurality of axial slots in communicationwith retaining channel portions above the retaining lip. The axial slotsare located and dimensioned to be complementary to the retaining tabs ofthe filter cartridge. The filter cartridge is retained to the base byaxially aligning the tabs with the slots and upwardly displacing thecartridge into the receptacle of the base. The cartridge is then rotatedso that the tabs are engaged within the retaining channel portions. The'188 patent discloses that compatibility of the cartridge with the basemay be ensured by providing the received portion of the cartridge witharcuate slots to accommodate keys axially projecting from the base asdisclosed in the '797 patent. Alternatively, the received portion of thecartridge may be provided with radial protrusions such as thosedisclosed in the '463 patent. Tracks in the base for receiving theprotrusions must be L-shaped (have an axial portion and a radialportion) to accommodate rotation of the cartridge relative to the base.

[0012] Ensuring filter cartridge compatibility is an issue of continuingconcern in the art. While the approaches to ensuring filter cartridgecompatibility described in the '797, '137, '463, and '188 patentsrepresent significant advances over the prior art, further improvementsin effectiveness and efficiency are possible. For example, keysprojecting from the base that require openings in the filter cartridgecompromise the sealed integrity of the filtration system. Keyingarrangements that restrict the cartridge to a fixed angular positionrelative to the base are incompatible with filter assemblies thatrequire rotation of the cartridge relative to the base. The L-shapedtracks disclosed in the '188 patent may be difficult to produce, therebyincreasing the cost of filter assemblies.

[0013] There is an ongoing need in the art for a filter assembly thatprevents installation of incompatible filter cartridges. Ideally, afilter cartridge compatible with such a key system may be employed witha filter assembly in which the cartridge is retained to the base by acollar and filter assemblies in which the cartridge is rotated to engageradially projecting tabs in a retainer fixedly extending from the base.

SUMMARY OF THE INVENTION

[0014] A first aspect of the present invention pertains to inward andoutward displacement of a roll seam at the junction of housing sectionsof a filter cartridge to provide components of a cartridge compatibilitymatrix. Portions of the roll seam are radially outwardly offset to formretention tabs. Further portions of the roll seam are radially inwardlydisplaced relative to the remainder of the roll seam. In one embodiment,the cartridge housing is substantially symmetric about a central axis,and the retention tabs are equiangularly spaced about the axis. The tabsare also substantially equivalent in angular extent and radialdisplacement, i.e., the tabs have the same general configuration.Consequently, the roll seam includes three substantially equal lengthportions extending between the retention tabs. One or more of these rollseam portions may include a segment that is inwardly displaced withrespect to the central axis. The receptacle of a compatible base isprovided with structures permitting reception and sealing of a cartridgewith a complementary pattern of retention tabs and inward displacedsegments. A non-compatible cartridge, for example a cartridge with asimilar arrangement of retention tabs but lacking the requisite inwardlydisplaced segments of the roll seam, is prevented from mating with thebase.

[0015] In a base with a fixed retainer where the retention tabs areaxially received through slots and the cartridge secured to the base byrotation relative to the base, compatibility is ensured by inwardprotrusions on the retainer lip. The inward protrusions of the retaininglip correspond to the inwardly displaced segments of the roll seam andallow axial reception of the roll seam through the retaining lip. Theroll seam of an incompatible filter cartridge will lack the correctarrangement of inwardly displaced portions of the roll seam will beprevented from axial reception into the base. In one cartridgecompatibility matrix, the roll seam includes three equiangularly spacedretention tabs and three equiangularly spaced inwardly displacedsegments of the roll seam. Alternatively, the inwardly displacedportions may be non-symmetrical to ensure a particular installedorientation of the cartridge relative to the base.

[0016] In addition, the filter cartridge may also comprise at least oneoutward protrusion from the side wall of that portion of the cartridgereceived in the base. Rather than an L shaped track in the basereceptacle, a ring at the entrance to the receptacle defines axialopenings compatible with the protrusions on the cartridge. Together, theconfiguration of the roll seam and the received portion of the cartridgemay be incorporated into multiple levels of keying for cartridgeidentification, cartridge positioning and quality control purposes.

[0017] Another aspect of the present invention relates to a filterassembly where a cartridge of the present invention is retained to abase by a collar. An annular lip of the base axially protrudes into aspace defined between the roll seam and the received portion of thefilter cartridge. The configuration of this space is complementary withthe configuration of the roll seam, e.g., the retention tabs increasethe radial dimension of the space and the inwardly displaced segments ofthe roll seam decrease the radial dimension of the space. The axiallyprotruding lip of the base is provided with outward protrusionscomplementary with the retention tabs and locations where lip materialis removed to accommodate inwardly displaced segments of the roll seam.

[0018] An object of the present invention is to provide a new andimproved filter cartridge compatibility matrix.

[0019] Another object of the present invention is to provide a new andimproved filter cartridge structure that ensures compatibility in filterassemblies having fixed and movable cartridge-retention systems.

[0020] A further object of the present invention is to provide a new andimproved filter assembly in which compatibility protection cannot bedefeated by omission of the compatibility matrix structure from thecartridge.

[0021] Other objects and advantages of the invention will becomeapparent from the drawings and the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention may be better understood and its numerousobjects and advantages will become apparent to those skilled in the artby reference to the accompanying drawings in which:

[0023]FIG. 1 is a vertical sectional view, partly broken away, of a fuelfilter cartridge incorporating a compatibility matrix exemplary ofseveral aspects of the present invention;

[0024]FIG. 2 is a top plan view of the filter cartridge of FIG. 1;

[0025]FIG. 3 is an enlarged view of an inwardly displaced segment of theroll seam of the filter cartridge of FIG. 2;

[0026]FIG. 4 is an enlarged sectional view through the roll seam at theleft side of the filter cartridge of FIG. 1;

[0027]FIG. 5 is an enlarged portion of the filter cartridge shown inFIG. 2 illustrating a retention tab formed from an outward deformationof the roll seam;

[0028]FIG. 6 is a front view of a portion of a first filter basecomponent configured to receive the filter cartridge of FIG. 1;

[0029]FIG. 7 is a side view of the filter base component of FIG. 6;

[0030]FIG. 8 is a top view of the filter base component of FIG. 6;

[0031]FIG. 9 is a sectional view of the filter base component of FIG. 6,taken along line 9-9 thereof;

[0032]FIG. 10 is a bottom view, partly in phantom, of the filter basecomponent of FIG. 6;

[0033]FIG. 11 is a sectional view of the filter base component of FIG.6, taken along line 11-11 thereof;

[0034]FIG. 12 is a side view of a second filter base componentconfigured to receive the filter cartridge of FIG. 1;

[0035]FIG. 13 is a bottom view of the filter base component of FIG. 12;

[0036]FIG. 14 is bottom view, partly in phantom, of a retaining collarfor retaining the filter cartridge of FIG. 1 to the base component ofFIGS. 12 and 13; and

[0037]FIG. 15 is a sectional view of the collar of FIG. 14, taken alongline 15-15 thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Preferred embodiments of a filter cartridge illustrating severalaspects of the present invention will now be described with particularreference to FIGS. 1-5. A first embodiment of a filter base componentcompatible with the cartridge of FIGS. 1-5 is shown in FIGS. 6-11. Asecond embodiment of a filter base component compatible with thecartridge of FIGS. 1-5 is shown in FIGS. 12-15.

[0039]FIG. 1 is a sectional view through an exemplary filter cartridge10 comprising a first housing section 12 joined to a second housingsection 14 along a peripheral roll seam 16. FIG. 4 illustrates anenlarged sectional view through the roll seam 16 on the left hand sideof FIG. 1. The sheet metal of the respective housing sections whichforms the roll seam is shown as dotted lines to the left and right ofthe filter cartridge 10 adjacent the roll seam in FIG. 1. The sheetmetal extending from the housing first section 12 extends radiallybeyond the sheet metal of extending from the housing second section 14.When rolled together to form the roll seam shown in FIG. 4, the extendedradial length of the sheet metal of the housing first section 12 isrolled under and overlaps the sheet metal of the housing second section14. The rolled, overlapping sheet metal is then crimped to form the rollseam in a manner known in the art. A U-shaped bend in the housing firstsection 12 inwardly of the roll seam defines a space 20 between the rollseam and the housing first section 12. This space 20 allows access tothe interior of the roll seam 16 during seam formation and for thepurposes of deformation as will be discussed below.

[0040] The filter cartridge 10 has an overall general configuration andfunctionality that is well understood by those of skill in the art. Afilter element 18 is supported within the filter cartridge. A grommet 30surrounds an axial opening 32 in the housing first section 12 thatreceives coaxial conduits (not shown) for delivery of unfiltered fluidand retrieval of filtered fluid from the filter cartridge 10. Thehousing second section 14 may be provided with a drain cock 60 forremoval of water that may accumulate in a sump 15 defined by the lowerportion of the housing second section 14.

[0041]FIG. 2 is a top view of the filter cartridge of FIG. 1. The rollseam 16 circumscribes the filter cartridge 10 radially separated fromthe housing first section 12 to define an annular space 20. The rollseam 16 includes three portions that are radially outwardly displacedrelative to the central axis A of the cartridge to form retention tabs24. The retention tabs 24 are illustrated as being equiangularlyarranged on the circumference of the roll seam and of equal angularextent and radial displacement. Three roll seam portions 23 extendbetween the retention tabs 24. In the illustrated embodiment, each ofthese portions 23 of the roll seam include a radially inwardly displacedsegment 22. The inwardly displaced segments 22 provide one variable foruse in conjunction with a cartridge compatibility matrix. The inwardlydisplaced segments 22 of the roll seam 16 on the exemplary filtercartridge 10 are diametrically opposed to each retention tab 24.

[0042] The inward and outward displacement of the roll seam relative toits generally circular shape result in a serpentine configuration. Thiscomplex shape is advantageously located at the radial outer periphery ofthe filter cartridge. As will be discussed in greater detail below, acompatibility matrix including a serpentine, or convoluted outerperiphery of the filter cartridge presents unique opportunities forblocking reception of cartridges omitting portions of the compatibilitymatrix. Further, inward and outward displacement of the roll seam 16relative to the central axis A of the cartridge defines an annular space20 having a variable radial dimension when measured perpendicular to thecartridge axis A, as best seen in FIG. 2. The shape of the annular space20 may be used as part of a cartridge compatibility matrix when thecartridge 10 is mounted to a base including the component shown in FIGS.12 and 13 by the collar shown in FIGS. 14 and 15. In accordance with afurther aspect of the present invention, the outer profile of the rollseam 16 is used as a constituent of a cartridge compatibility matrixwhen the cartridge 10 is mounted to a base including the component shownin FIGS. 6-11.

[0043]FIG. 3 illustrates an enlarged view of an inwardly displacedsegment 22 of the roll seam 16. In the illustrated embodiment, theinward displacement of the roll seam is in the form of an arc having aradius of curvature of approximately 2.5″ and a center of curvaturelocated outside the roll seam 16. The inward deformation displaces theroll seam 16 inwardly from its normal radius of curvature 17(illustrated by the dashed line in FIG. 3) by a distance in the range of0.02″ to 0.05″ at the center of the deformation. The inwardly displacedsegment has a length of approximately 0.5″ measured along thecircumference of the roll seam.

[0044]FIG. 5 is an enlarged portion of FIG. 2 illustrating the outwarddisplacement of the roll seam 16 to form a retention tab 24. The rollseam is radially outwardly displaced by a distance of approximately0.08″ relative to adjacent portions of the roll seam or a distanceapproximately equivalent to the radial thickness of the roll seam 16.Each retention tab 24 of the illustrated embodiment maintains itsmaximum outward displacement (of approximately one roll seam thickness)for approximately 0.5″. It will be appreciated that the roll seam 16includes transitional portions 24 a adjacent either end of the retentiontabs. The roll seam 16 between the retention tabs 24 (including theirtransitional portions 24 a) and the inwardly displaced segments 22maintain a substantially constant radius of curvature centered on thecartridge axis A.

[0045] FIGS. 6-11 illustrate one component of a first embodiment of afilter base configured to mount the filter illustrated in FIGS. 1-5. Theillustrated component 40 of a filter base is a molded member withintegrally extending bracket portions 42. The bracket portions 42 areconfigured to receive a reinforcing metal sleeve (not shown) throughwhich an attachment bolt (not shown) retains the filter base to asupport structure (not shown). Below the bracket portions, theillustrated base component 40 comprises a generally cylindrical wall 46that defines a receptacle 47 for axially receiving the filter cartridgehousing first section 12. An axial central conduit 48 of the basecomponent 40 is received and sealingly engaged by a grommet 30 of aninstalled filter cartridge 10. The cylindrical wall 46 flares to includea fixed integral retainer 44. The retainer 44 comprises three axialslots 51 complementary to the radially projecting retention tabs 24 onthe cartridge 10. The axial slots 51 communicate with retaining channelportions 43 partially defined by a retaining lip upper surfacecomprising a ramp 52 and a seat 54.

[0046] The first housing section 12 of the filter cartridge 10 isaxially inserted into the receptacle 47 until the retaining tabs 24 arealigned with the retaining channel portions 49. The cartridge 10 is thenrotated clockwise relative to the base. During rotation, the retainingtabs ride up the ramps 52 and over a raised portion of the retaining lipto seats 54 defined by the retaining lip upper surface. A resilientradial extension 34 of the cartridge grommet 30 biases the cartridge 10away from the base component 40 so that the seated retention tabs 24resist unintended counterclockwise rotation of the cartridge 10 relativeto the base.

[0047] In accordance with an aspect of the present invention, theretainer 44 defines lip portions 72 having an inward-facing profileincluding radially inward projecting protrusions 56 corresponding to thelocation of each inwardly displaced segment 22 of the roll seam 16relative to the retention tabs 24 (the location of which correspond tothe axial slots 51 separating the retaining lip portions 72). The axialslots 51 and lip portions 72 with protrusions 56 code the base component40 for a filter cartridge such as cartridge 10 with a roll seam having acompatible pattern of retention tabs 24 and inwardly displaced segments22. The roll seam 16 of a compatible filter cartridge can pass theretaining lip portions 72, permitting complete axial reception of thecartridge housing first section 12 into the receptacle 47 so thatsubsequent rotation of the cartridge mounts the cartridge to the base.An incompatible cartridge (lacking, for example, the requisite inwardlydisplaced segments 22) is blocked from axial reception and cannot bemounted to the coded base.

[0048]FIGS. 12 and 13 illustrate a second representative embodiment of abase component 80 configured to receive a cartridge illustrated in FIGS.1-5. This form of filter base comprises a cast or molded component 80with a cylindrical wall 92 defining a receptacle 87 into which thehousing first section 12 of the cartridge is axially receivable. Thecartridge is retained to the base by a collar 100 (illustrated in FIGS.14 and 15) that engages the peripheral roll seam 16. In accordance withan aspect of the present invention, the end 82 of the wall 92 isprovided with a sectional configuration complementary to the annularspace 20 defined between the cartridge housing first section 12 and theroll seam 16. Radial outward projections 84 of the lip correspond to thelocation and outward radial displacement of the retention tabs 24. Thebase component 80 may be cast with the lip 82 having locations 86 wherethe lip is thinned or notched to accommodate inwardly displaced segments22 of the cartridge roll seam 16. Alternatively, lip material may beremoved after production of the base component 80, such as by machiningthe lip at locations 86.

[0049] The collar 100 includes an inward projecting thread 108configured to engage an outward projecting thread 88 on the basecomponent 80. Rotation of the collar 100 relative to the base component80 causes the collar thread 108 to ride the base thread 88, bringing thecollar retaining lip 102 to bear against the radially projecting rollseam 16 of the cartridge 10. A spring (not shown) in the base receptacle87 biases the cartridge 10 and collar 100 away from the base componentto maintain the collar in a locked position over the end of the basethread 88. This mounting system requires that the axially projecting lip82 of the base component be received in the annular space 20 with roomfor axial movement to accommodate compression and release of the springas the collar thread 108 rides up and over the thread 88 of the base. Arigid abutment of the cartridge roll seam 16 against the lip 82 of thebase that prevents the necessary axial movement of the cartridge 10relative to the base component 80 will prevent complete rotation of thecollar 100 to its locked position.

[0050] The lip 102 of the collar 100 includes a plurality of locations103 where the lip and adjacent structure is recessed or lip material isremoved to accommodate the shape 13 (an outward deflection best seen inFIG. 1) of the cartridge housing second section 14 adjacent the outwarddeformation of the roll seam 16 for each retention tab 24. In theillustrated embodiment, the collar is provided with six locations 103where lip material is removed. The six locations 103 correspond to thesix possible engaged positions of the collar 100 relative to the basecomponent 80 and the received filter cartridge 10. The outwarddeflections of the housing second section fit into three of the sixlocations, further enhancing the security of the collar 100 in itslocked position relative to the cartridge 10 and the base component 80by resisting unintentional reverse rotation of the collar.

[0051] A filter cartridge lacking outward deformations 24 of the rollseam 16 complementary to the outward projections 84 on the axiallyprojecting lip 82 of the base component 80 will be blocked from axialreception and mating with the base. Similarly, filter cartridgesincluding inward deformations of the roll seam will be rejected by abase whose axially projecting lip 82 does not include locations 86 wherelip material has been removed to accommodate them. By axial receptionand mating with the base, it is meant that the grommet 30 carried by thehousing first section 12 fully engages the axial conduit 88 of the basecomponent and the lip 82 of the base is received in the annular space 20of the cartridge with room to move axially during rotation of the collar100 to its locked position. Thus, the configuration of the axiallyprojecting lip 82 forms a component of a cartridge compatibility matrixthat codes the base for a cartridge having a particular shape of annularspace 20 (as defined by deformations 24, 22 of the roll seam).

[0052] A further aspect of the present invention contemplates a filtercartridge compatibility matrix comprising the roll seam retention tabs24 and inward displaced segments 22 as described above and furtherincluding radial protrusions 28 of the cartridge housing section firstend 12. In the first embodiment of a filter base component 40, a ring(not shown) is keyed to the base component to define an entrance to thereceptacle 47. The ring includes openings that allow axial passage ofthe radial protrusions 28 of the housing first section 12. Once theradial protrusions 28 are axially past the ring, the receptacle 47 ofthe base component 40 permits rotation of the cartridge relative to thebase. Radial protrusions 28 of the housing first section 12 may be usedas an additional component of the cartridge compatibility matrix. Theradial protrusions may also be employed to ensure a particular installedorientation of the cartridge 10 relative to the base component 40.

[0053] The inside surface of the wall 92 defining the receptacle 87 ofthe second embodiment of a filter base component 80 may include axialtracks (not shown) complementary to the pattern of radial protrusionsfrom the cartridge housing first section 12. The tracks may be moldedand/or machined on the inner surface of the receptacle of the basecomponent 80. A filter cartridge including an incompatible pattern ofradial protrusions will be blocked from axial reception into thereceptacle 87. In combination, the configuration of the filter cartridgeroll seam 16 and received housing first section 12 can be used to ensurefilter compatibility and a particular installed configuration of thefilter cartridge 10 relative to the base component 80.

[0054] While preferred embodiments of the present invention have beenset forth for the purposes of illustration, the foregoing descriptionsshould not be deemed a limitation of the invention herein. Accordingly,various modifications, adaptations and alternatives may occur to oneskilled in the art without departing from the spirit and the scope ofthe present invention.

What is claimed is:
 1. A filter cartridge comprising: a filter elementarranged around a central axis; and a housing for said filter element,said housing comprising first and second sections having respectivefirst and second diameters relative to a central axis, said seconddiameter being greater than said first diameter, said first sectionsurrounding an axial end of the filter element and defining an axialopening and joined to said second section along a radially projectingshoulder, wherein said shoulder has a primarily circular outer profile,said primarily circular outer profile being interrupted by angularlyspaced retention tabs projecting radially outwardly relative to saidprimarily circular outer profile and at least one profile segment havinga reduced radial distance from the central axis relative to theprimarily circular outer profile.
 2. The filter cartridge of claim 1,wherein said shoulder comprises a roll seam formed at the junction ofsaid first and second sections.
 3. The filter cartridge of claim 1,wherein said first section comprises an axially extending generallycylindrical wall and said shoulder is radially spaced from saidcylindrical wall to define a substantially annular space.
 4. The filtercartridge of claim 3, wherein said substantially annular space comprisesfirst, second and third portions having respective first, second andthird radial dimensions, said first radial dimension corresponding to afirst radial distance between the cylindrical wall and the primarilycircular outer profile, said second radial dimension corresponding to asecond radial distance between the cylindrical wall and each of theretention tabs and said third radial dimension corresponding to a thirdradial distance between the cylindrical wall and the profile segmentshaving a reduced radial distance from the central axis relative to theprimarily circular outer profile, said first radial distance being lessthan said second radial distance and greater than said third radialdistance.
 5. The filter cartridge of claim 1, comprising three retentiontabs equiangularly arranged around a circumference of said shoulder. 6.The filter cartridge of claim 1, wherein said at least one profilesegment is angularly spaced from said retention tabs.
 7. The filtercartridge of claim 1, comprising three retention tabs equiangularlyarranged around a circumference of said shoulder and said at least oneprofile segment comprises three profile segments, each of said threeprofile segments diametrically opposed to a retention tab.
 8. The filtercartridge of claim 1, wherein said at least one profile segmentcomprises an arc having a center of curvature outside said substantiallycircular profile.
 9. The filter cartridge of claim 1, wherein said atleast one profile segment comprises a substantially linear portion ofsaid shoulder between two angularly spaced points on said substantiallycircular profile.
 10. A filter cartridge comprising: a filter elementextending between axially separated first and second ends; a housingfirst section defining a portion of a cylindrical space and supportingthe first end of the filter element, said housing first section having afirst end defining an axial opening, a generally cylindrical side wallextending from the first end to a second end including a U-shaped bend;a housing second section defining a portion of the cylindrical space,said housing second section having a first end joined to the housingfirst section second end by a roll seam, the second end of the housingsecond section surrounding the second end of the filter element, whereinsaid roll seam is radially spaced from the side wall of the housingfirst section to define a substantially annular space, said annularspace comprising portions having first, second and third radialdimensions relative to the side wall, said first dimension being smallerthan said second and third dimensions and said second dimension beingsmaller than said third dimension.
 11. The filter cartridge of claim 9,wherein said substantially annular space comprises three retaining tabportions having said third dimension, three inwardly displaced portionshaving said first dimension angularly spaced from said retaining tabportions and six intermediate portions having said second dimension,said intermediate portions arranged between said retaining tab portionsand said inwardly displaced portions.
 12. The filter cartridge of claim10, wherein said retaining tab portions alternate with said inwardlydisplaced portions.
 13. A filter cartridge comprising: a filter element;a housing for said filter element, said housing comprising first andsecond sections and a central axis; said first section defining an axialopening and joined to said second section along a circumferential rollseam; said roll seam comprising alternating radial inner and outerarcuate segments, said inner segments having substantially equal radiiof curvature, wherein an arc defined by the roll seam of at least one ofsaid inner segments is interrupted by a portion of said roll seamradially inwardly displaced relative to said radii of curvature.
 14. Thefilter cartridge of claim 13, wherein said portion comprises asubstantially linear segment of said roll seam between two angularlyoffset points on said arc.
 15. The filter cartridge of claim 13, whereinsaid portion comprises a substantially arcuate inward deflection of saidroll seam between two angularly offset points on said arc.
 16. Thefilter cartridge of claim 13, comprising three inner segments and threeouter segments.
 17. The filter cartridge of claim 16, wherein the threeinner segments have equivalent first arcuate extents and said threeouter segments have equivalent second arcuate extents, said firstarcuate extents subtending a greater angle than said second arcuateextents.
 18. The filter cartridge of claim 16, wherein each of saidthree inner segments is interrupted by a portion of said roll seamradially inwardly displaced relative to the first radii of curvature.19. The filter cartridge of claim 18, wherein each of said three innersegments is bisected by the portion of said roll seam inwardly displacedrelative to the first radii of curvature.
 20. The filter cartridge ofclaim 15, wherein said arcuate inward deflection has an axis ofcurvature outside said circumferential roll seam.
 21. A method formanufacturing a filter cartridge comprising the steps of: forming a rollseam at the junction of first and second cartridge housing portions,said roll seam having a substantially constant radius of curvature;displacing at least a first portion of said roll seam radially outwardlyrelative to said radius of curvature; and displacing at least a secondportion of said roll seam radially inwardly relative to said radius ofcurvature.
 22. The method of claim 21, wherein said step of displacingat least a first portion comprises displacing three first portions ofsaid roll seam radially outwardly relative to said radius of curvature.23. The method of claim 22, wherein said three first portions areequiangularly arranged around an axis of said filter cartridge and havesubstantially equivalent arcuate extents.
 24. The method of claim 23,wherein said step of displacing at least a second portion comprisesdisplacing three second portions of said roll seam radially inwardlyrelative to said radius of curvature.
 25. The method of claim 24,wherein said three second portions are equiangularly arranged around anaxis of said filter cartridge and are of substantially equivalentconfiguration.
 26. The method of claim 21, wherein said step ofdisplacing at least a first portion comprises displacing said at least afirst portion radially outwardly by a distance of approximately 0.08″relative to a central axis of said cartridge.
 27. The method of claim21, wherein said step of displacing at least a second portion comprisesdisplacing said at least a second portion radially inwardly by adistance in the range of 0.02″ to 0.05″ relative to a central axis ofsaid cartridge.